<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    .active {
      color: red
    }
  </style>
</head>
<body>
<div id="app">
  <h2 :class="['active', 'line']">{{message}}</h2>
  <h2 :class="[active, line]">{{message}}</h2>
  <h2 :class="getClasses()">{{message}}</h2>
</div>

<script src="../js/vue.js"></script>
<script>
  const app = new Vue({
    el: '#app',
    data: {
      message: '你好啊',
      active: 'aaa',
      line: 'line'
    },
    methods: {
      getClasses: function () {
        return [this.active, this.line]
      }
    }
  })
</script>
</body>
</html>
